One of the benefits of running digital, is that in theory only two cables to the track are needed. All other devices, locos, turnouts, signals, light may be connected to the track to get their power there, and their control signals too through a decoder, which may be installed in the turnout or signal itself.

There is only one problem, the power. To avoid to destroy equipment, the power is limited to about 40 - 50 VA maximum. So the power consumers must be separated into different circuits, each fed from its own power source. It may be done with minimizing the cables again, by using booster, and digital "power" in each circuit, or by separating the power consumers into groups needing digital power, and groups content with pure AC. This alternative needs more cabling but is much cheaper.

To get this work, always remember one simple thing; each circuit should have a common ground. Or, the "brown" of all circuits, should be connected together.

Boosters The current from the digital system to the track is really a mix of a signal and power; the signal is understood by the decoders, the power is needed by the motors and lamps connected to the track. A booster is easily described; it is a device which takes the AC power from a transformer, and the signal from a digital central unit, mixes them, and feeds a digital circuit. Real boosters don't have any logic which understands the signal, so it's possible to use booster for different protocols, provided they don't differ in electrical portions. And it's important that the power from this booster is in phase with the power from the central unit and other connected boosters; otherwise the pickup shoe of the locos when passing from one section to another would case a short of 2*24 V and probably cause some damage.

Three different types of boosters for Märklin are mentioned here, but it should be possible to use also booster from other makes, or a home-built one.

The first is the standard booster, not much to say about it. It takes advantage of a 52 VA transformer and delivers about 47 VA.

The second is a smart and cheap thing. The DELTA Control may be used as a booster, if the knob is set to the rightmost position, the DELTA Pilot connections are connected together, the red cable connected to the digital signal of the Central unit. It delivers maximum about 30 VA, and is much cheaper than the standard booster.

The third isn't a real booster. If you use the Intellibox from Uhlenbrock as your central unit, you may use a Märklin CU like 6020 or 6021 as a kind of booster. In this case the Intellibox pretends it is a computer interface to the central unit, and send commands to it and receives control commands too. This makes it possible to have a digital circuit at the output of the 6020 or 6021, suitable to control accessories. But the signal is not in phase with the Intellibox signal, and it's protocol is limited to what the 6020 or 6021 understands, so loco control is not recommended. You may say that the Märklin CU has the function of a booster, but it works differently.

AC for locos It's possible to feed some tracks with AC, most decoder will understand this signal and the train will continue with a speed corresponding to the voltage of the section. However, newer delta decoders will not, and a special isolation is needed between the digital and the AC section, so this is not recommended. AC for accessory control Just because you have chosen digital operation of your locos, that doesn't mean you have to operate your turnouts and signals with digital signal. Do you use a DELTA system? Then it's not possible to control them digitally at all, so connect all those to a separate AC circuit, and control them traditionally. Remember common ground; the lamps in the turnouts of M-track are grounded through the rail, so they won't be lighted if you forget it.

And you may have a mixture. Some turnouts and signals on the main line may be controlled by a computer, so the must have a decoder and digital signal. Others, like at the yard, may as well be controlled conventionally, by an AC circuit.

Accessories are not power consumers, as only one at a time normally is switched. But if they bear lamps, they get the power through the decoder too, see more below.

AC for lamps Pure lamps may of course be fed by AC. This includes lamps in turnouts and signals. If these are controlled digitally, the yellow cables for the lamp and for the coils should be separated. With 72xx signals, and C-track/K-track turnouts this is no problem, as they have two yellow connections. M-track turnouts with light, and 70xx signals need some (easy) surgery to separate those. I used a black cable to feed the light of my turnouts!



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